Single retrieval trial alone did not enhance fear extinction. (A) Freezing during tone-cued fear conditioning in Day 1. (B) Freezing in the extinction context. Single CS presentation (180 sec) was given only to the retrieval group but not to the nonretrieval group. (C) Within-session fear extinction after the single retrieval trial. The retrieval group received 12 1-min tones at 2-min intervals, and the nonretrieval group received 15 tones. (D) Fear extinction memory test for spontaneous recovery in the extinction context. Animals were given a single 3-min tone after 3 min of acclimation. (E) Fear renewal test conducted in the fear acquisition context. On Day 4, animals were returned to the fear acquisition chamber and received a single 3-min tone presentation. Retrieval group, n = 10; nonretrieval group, n = 10.
